Effect of the structure of bridging ligands on the structure and adsorption properties of 3D-coordinated copper(II) and cobalt(II) formate polymers

Abstract

Increasing length of the bipyridyl bridging ligands in a series of similar complexes facilitates the formation of microporous coordination polymers. The structure of one of these compounds was found by the Rietveld method. These compounds were found to differ in their adsorption caparcities relative to methanol, nitrogen, and hydrogen.Porous inorganic materials have found common use as adsorbents, catalysts, inert supports for catalysts, and working bodies in sensor devices [1]. Recently, in addition to the study of porous materials derived from p-elements such as porous silica, alumosilicas, and alumophosphates or other elements such as charcoals, greater attention has been given to a relatively new class of porous polymers, namely, porous coordination polymers (PCP) [2]. As a rule, PCP consist of unit blocks (metal ions) and ligands joining these blocks. The size and shape of the PCP pores are a function of the coordination number and coordination polyhedron topology of the complexing metal ion and the structure of the bridging ligands, especially, the arrangement of the donor groups and the distance between these groups. Variation of the metal ion or ligand permit us to control the pore size and adsorption capacity of PCP although it is not always possible to predict how the change in the metal coordination number or ligand will affect the structure of the coordination polymer. For example, in some cases, increasing length of the bridging ligands leads to a corresponding increase in the polymer pore volume in a homologous series [2, 3] but also has no significant effect on pore volume [4].Copper(II) and cobalt(II) formates are capable of forming infinite 2D-M(HCO 2 ) 2 L 2 networks (L is a monodentate ligand such as formamide) consisting of cyclic M 4 (HCO 2 ) 4 fragments (M = Cu 2+ , Co 2+ ) [5]: 0040-5760/06/4201-0043

Effect of structural and thermodynamic factors on the sorption of hydrogen by metal–organic framework compounds

“…In the absence of specific interactions and of limitations in respect of the accessibility of the pores due to the size of the sorbate molecules analysis of the sorption isotherms of various substances (including nitrogen at 77 K, hydrocarbons and methanol at 298 K) gives very similar values [40]. The possibility of specific interactions is determined by the chemical nature of the sorbate and the surface and by the ability to form chemical (most often hydrogen) bonds between the molecules of the sorbate and the sorbent [41,42]. It is also worth mentioning that in the case where DG for the specific interactions is comparable with DG for the structural or conformational rearrangement of the MOF the adsorption of the substrate can be accompanied by an increase in the volume of the pores (the effect of "breathing" or swelling of the sample).…”

“…It is also worth mentioning that in the case where DG for the specific interactions is comparable with DG for the structural or conformational rearrangement of the MOF the adsorption of the substrate can be accompanied by an increase in the volume of the pores (the effect of "breathing" or swelling of the sample). These factors can be of enormous significance during determination of the characteristics of a substance -the sample may sorb perceptible amounts, for example, of methanol (capable of forming hydrogen bonds with the lattice of the sorbent) and not sorb hydrogen [41,43].…”